The present invention relates to a photosensitive composition which contains a diazonium salt polycondensation product and a polymeric binder and which is especially suitable for the production of printing plates.
German Offenlegungsschrift No. 30 36 077 (equivalent to U.S. Pat. No. 4,387,151) disclosed photosensitive compositions comprising co-condensation products of condensable diazonium salts and other non-photosensitive condensable compounds combined with polymeric binders containing alkenylsulfonylurethane side groups, which are used for the production of printing plates. These compositions can be developed with purely aqueous, alkaline solutions. However, when these compositions are processed into lithographic printing plates, they yield light-hardened layers having an insufficient ink receptivity.
In German Offenlegungsschrift No. 24 29 251 similar photosensitive compositions are described, the binders of which comprise organic synthetic resins with free hydroxyl or carboxyl groups, which have been reacted with polyvalent isocyanates, epoxides or acid anhydrides as crosslinking agents. Some of these compositions still contain unreacted crosslinking groups and others contain insoluble constituents, such that their storage stability and developability are limited.
European Patent Application No. 152 819 discloses photosensitive compositions comprising diazonium salt polycondensation products and binders containing carboxyl groups, which have been obtained by reacting polymers containing hydroxyl groups with acid anhydrides. These compositions can be developed with aqueous-alkaline solutions and are suitable for use in the production of lithographic printing plates yielding large print runs. As it is desired to further increase the print runs obtained from printing plates produced with these compositions, European Patent Application No. 152 819 recommends addition of relatively small amounts of other polymers, e.g., polyurethanes, to the compositions to improve their resistance to abrasion. However, this combination leads to disadvantages in view of copying technique, for example, to an undesirable rise of tonal value. In addition, developability and storage stability are impaired.
U.S. Pat. No. 3,660,097 and German Offenlegunsschrift No. 27 39 774 also disclose compositions of the above-indicated type, in which polyurethane resins are used as the polymeric binders. These compositions have the disadvantage that the binder are insufficiently soluble in the customarily employed coating solvents and the solutions must be repeatedly filtered to remove insoluble residues. The developability of these compositions in aqueous-alkaline solutions is extremely limited and the print runs obtainable are inadequate for high-performance printing.
European Patent Application No. 0 030 001 describes a similar composition which contains a branched polyurethane as the binder. Although relatively large print runs can be obtained with the aid of this composition, it also has some disadvantages. Acidic aqueous developer solutions should, for example, preferably be used for scrum-free, speedy development of the light-hardened layer and, in the case of automatic processing, these developer solutions may give rise to corrosion problems affecting the light metal parts of processors.